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11.3.14

It’s about that time, boys and girls. A new “protein kills” study has
arrived to throw you into the pit of existential angst and self-doubt
you recently managed to crawl out of from the last one. As you may know,
I’ve just spent a week in Tulum, Mexico for PrimalCon
(which was amazing, by the way, absolutely fantastic) where I managed
to avoid most contact with my inbox. Oh, I took a couple glimpses here
and there, enough to notice an endless stream of frenzied email subject
lines, but I didn’t read the contents until the flight home. I still
knew what was coming.

I finally have a little time to dig into this paper (which actually
covers two studies) to see if there’s anything we can learn. Let’s jump
right in…

Mark,

A co-worker informed me of a news clip she’d heard regarding an
increased cancer risk for those who stick to a high animal protein-based
diet. She said that smoking cigarettes is healthier than eating high
fat/high protein diet. My first reaction was to chuckle (just another CW
media attack against Paleo/Primal) and I did once I read the actual piece in Forbes.
I wanted to get your thoughts on it as a lot of the article’s evidence
once again seems inconclusive. Seems like there are a lot of caveats.

Emily

Right off the bat, we can read the paper and see an important part that the journalists conveniently left out:

Conversely, high protein intake was associated with
reduced cancer and overall mortality in respondents over 65, but a
5-fold increase in diabetes mortality across all ages.

and:

Using Cox Proportional Hazard models, we found that high
and moderate protein consumption were positively associated with
diabetes-related mortality, but not associated with all-cause, CVD, or
cancer mortality when subjects at all the ages above 50 were considered.

Huh. From age 50-65, protein modestly increases mortality, especially
cancer- and diabetes-related mortality. In ages 50+, though, a high
protein intake has no association with all-cause mortality (the most
important endpoint), while in ages 65+, high protein is downright
protective. The only consistent positive association across all ages is
with diabetes mortality. How can this be?

It’s well known that seniors are less efficient at utilizing protein
than younger people. Muscle protein synthesis is slightly impaired in
the elderly, for example. As such, they need to eat more of it to get
the same benefits as the rest of the population. It may be that they
also have a higher upper threshold for protein until harm ensues – a higher “protein ceiling.”

Other populations also have higher ceilings. Runners, cyclists, dancers, swimmers, weight lifters (especially weight
lifters) all need more protein than the sedentary, just like the
seniors. Unfortunately, the authors did not control for exercise. Too
bad, because it probably would have modified the relationship between
protein intake and mortality in the other age groups.

I think if anything can be taken from this study, it’s that you
should only eat as much protein as you require. We likely all have “safe
protein ceilings” depending on various factors, like age and activity
level. The ceiling is higher the older and more active you are.

Since the connection between diabetes-related mortality and protein
persisted even among the older crowd, let’s look at that a little
further. Does other research agree that protein is bad for diabetics?

Well, in the most recent meta-analysis dealing with diet and diabetes,
researchers concluded that “low-carbohydrate, low-GI, Mediterranean,
and high-protein diets are effective in improving various markers of
cardiovascular risk in people with diabetes and should be considered in
the overall strategy of diabetes management.” They looked at both
epidemiology and clinical trials to reach that conclusion, so
it’s not clear how protein is increasing diabetes mortality in the
current study if the relationship is causal.

I’m not suggesting that you eat all the protein you want as long as you’re exercising or elderly. I’ve even softened my “high-protein” leanings over the years, advocating instead for a more moderate approach. One gram protein per pound of lean tissue is plenty for most active people, and many can get by on half that.

The Mouse Study

Okay, that’s one part of the paper. There was also a study that found
both breast cancer and melanoma tumors grew more slowly in mice on a
4-7% protein diet than mice on an 18% protein diet. High protein mice
also had higher levels of IGF-1, a growth promoter, and the rate of
tumor growth was associated with the amount of IGF-1 secreted. The
protein was entirely casein, with a touch of added methionine.

When I saw that they used casein, it reminded me of something from Chris Masterjohn’s analysis of the T. Colin Campbell casein/cancer studies.
While high intakes of casein promoted the growth of existing tumors in
those rodents, it was also protective against the mutagens that cause
the initial appearance of tumors. Protein was protective against cancer
until they had it, at which point it accelerated the cancer’s
progression. Rodents on the low protein diet were more susceptible to getting cancer after aflatoxin exposure. Once the rodents already had cancer, low protein was protective against further growth.

Does this phenomenon apply to the most recent study? Impossible to
tell. The mice were directly injected with melanoma and breast cancer
cells, not exposed to a cancer-causing toxin or exposed to high levels
of UV radiation. This usually isn’t how cancer develops in the real
world, unless we’re talking about mistakenly receiving a cancerous organ
transplant. We tend to develop cancer in response to mutagens in the
environment.

That said, we can’t discount the results entirely. Getting your protein only from casein
is unwise (and unfeasible when eating whole foods). Methionine (an
amino acid common in muscle meat which does increase IGF-1) probably
should be balanced with glycine (an amino acid common in connective
tissue and gelatinous cuts of meat). I think glycine is especially
important for a few reasons:

Glycine supplementation even mimics the life extending properties of methionine restriction.

Realize that the Primal eating plan doesn’t prescribe “eating lots of meat.” Instead, we “eat animals,” and animals have bones and gristle and organs and tendons and loins and ribs and shoulders and all kinds of edible bits and pieces with extremely varying amino acid profiles. Over the years, I’ve been emphasizing these “alternative” cuts
more and more. The folks profiled in the study’s data sets probably
weren’t eating whole animals. The mice definitely weren’t. We largely
just eat meat, and I think that should probably change if we want to
maintain optimal health and avoid some of the diseases the epidemiology
keeps pointing at.

There are also untoward effects of ultra-low protein intakes to
consider. While this paper was only concerned with the cancer endpoint,
free-living, free-thinking, autonomous humans with hopes, desires,
aspirations, and goals aren’t only worried about cancer. We’d certainly
prefer not to have cancer, but what if the narrow pursuit of
the ultimate anti-carcinogenic diet has unpleasant side effects that
affect the enjoyment of our lives?

In other words, starving yourself of protein (the mice in the study
achieved the protective effects by eating just 4-7% of calories as
protein, which qualifies as protein starvation in most books) may reduce
tumor growth, but it might make you fatter and weaker, give you brittle
bones, prevent you from taking care of yourself in the later years, and
make you more susceptible to illness. Oh, and it may even make you more
vulnerable to initiallygetting cancer (if the
Campbell casein studies are applicable to people). But that’s all worth
it if once you have cancer the tumors grow slightly more slowly, right?

Even IGF-1 isn’t evil. It promotes growth across the board – in muscles
and in tumors. Tumors suck, but not everyone has tumors. Everyone does
have muscles. IGF-1 secretion also promotes neural growth and resistance
to neurological degeneration. In a study mentioned in yesterday’s Weekend Link Love,
elderly women improved muscular and cognitive function by eating a diet
high in protein derived from red meat and lifting heavy things. Another study found
that increased IGF-1 was linked to improved memory and vigor in both
middle-aged and elderly subjects. I don’t know about you, but “living long and dropping dead” is all about vigor for me.

Think about it. Vigor. Sure, it’s not exactly a traditional health
biomarker, but who’s got it? What kind of older people display vigor?

How valid is the dietary data? It was gathered by calling people on
the phone and asking them what they’d eaten the previous day and whether
that was typical of their normal diet. Seems awfully unreliable and
prone to human error.

That’s my take. There are many others out there, but this is mine. What do you think?